Montgomery County's Coalition of Black Police Officers has filed a sweeping racial discrimination suit against the county government and its police force, claiming that prejudice has barred scores of blacks from being accepted on the force, or from being promoted.

In the suit filed last week in U.S. District Court in Baltimore, the black officers contend that the county is violating the federal Civil Rights Act of 1964, which forbids racial discrimination. The black officers are accusing the county of discriminating since only 5 percent of the police department's 800 officers are black. The county is about 10 percent black, and the percentage of blacks in the standard metropolitan statistical area used for census purposes is about 25 percent.

The suit, which includes County Executive Charles W. Gilchrist, Police Chief Bernard D. Crooke, and chief administrative office Robert Wilson as defendants, was filed on behalf of a broad group that includes current officers complaining of discriminatory promotion practices, black applicants who were denied entry into the department, and others who claim they were discharged because of poor performance ratings they did not deserve.

The black police officers are asking for back pay for black officers denied promotions, according to their attorney Donald Jones. Also, Jones said, the officers would like to see the county institute an affirmative hiring and promotion policy.

"We're not going to ask that anyone be bumped," Jones said. "But we're going to ask the county to come up with a plan . . . . we can get retroactive seniority at least, and at most an upgraded timetable for moving blacks through the department more quickly."

Any affirmative hiring program would likely meet stiff resistance from the police union, if other cities provide any example. In the District of Columbia, Mayor Marion Barry in 1981 proposed hiring police officers by a lottery system, to compensate for a test he thought was biased against blacks. But Barry was forced to retreat following opposition from the District's Fraternal Order of Police, which lobbied against the change with members of Congress.

DeVance Walker, Gilchrist's minority affairs adviser, said the executive has instituted an affirmative hiring policy that has substantially increased the number of black officers since 1980. Walker said there are now 51 black police officers, as well as three Hispanics, two Asians and three American Indians. In 1980, there were only 33 black officers, Walker said.

Walker did say that the last police training class, ending in October, included eight blacks out of a total of 39 applicants. Four of the eight, or about 50 percent, dropped out, he said.

Police Chief Crooke, in a statement, said that the civil rights division of the U.S. Department of Justice had reviewed the black officers' complaints and decided not to file the suit itself, as it could have under the Equal Employment Opportunity Act.

But William B. Fenton, deputy chief of the federal enforcement section of the Justice Department's civil rights division, said the department's decision not to sue "is no determination on the merits of the matter." Fenton said "we simply do not have the personnel to sue on all of the charges that are brought before the department ."

Montgomery's black officers are alleging that antiblack bias begins in the academy, where "exclusively white" instructors use "psychological intimidation, hostility, and racial stereotyping" to cause black applicants to drop out. The attrition rate for blacks is about 40 to 50 percent, the suit says, compared to about 5 percent for whites.

Discrimination continues through the black recruits' initial probation period, according to the complaint, which is often extended for blacks. Officers assigned to evaluate black rookies are almost always whites, the suit says, who use "groundless derogatory written comments, exaggerated criticisms, and give low ratings where none is deserved."

For the blacks who become officers, the suit alleges that racial bias continues when it comes to promotions. According to the suit, only three blacks have been promoted to sergeant or higher in the last 15 years.